1. Field of the Invention
The present invention relates to a manufacturing method of an electronic circuit device including a multi-layer circuit board incorporated with a thin film capacitor.
2. Related Art
Along with a reduction in size of portable equipments, a technique of incorporating passive components such as capacitors into substrates with an aim of an improvement in the mounting density has been popularized mainly in cellular telephones. At present, the use of ceramic substrates is the predominant technique; however, resin substrates with built-in passive elements have been noted as mounting substrates for electronic circuit devices since they are light in weight, not-chipped and inexpensive. In a case of incorporating capacitors in substrates, the use of thin film capacitors capable of increasing the capacitive density is advantageous for a reduction in size. Substrates with built-in capacitors and manufacturing methods thereof are described, for example, in Japanese Patent Publication No. Hei 7-16099 as the prior art. The constitution of the circuit package is to be described schematically for the portions relevant to this invention with reference to FIG. 4. A circuit package 101 comprises substrates 160, 161 with a thin film capacitor 141 being put between them. Further, the thin film capacitor 141 is formed integrally with the substrate 160. That is, as the feature of such a constitution, the thin film capacitor 141 is disposed in a manner as to be integrated with and buried in the circuit package 101. More specifically, a thin Cu film formed on the surface of a Teflon substrate or the like is fabricated by photolithography to constitute a desired circuit for a printed circuit board. In this case, at least a first wire 123 and a first electrode 125 connected therewith for the thin film capacitor 141 are formed. An epitaxial thin film 151 comprising dielectric material is formed by sputtering at least covering the first electrode. A Cu layer is formed on the thin film dielectric 151 and, successively, Cu plating is applied thereto. The thus formed thin Cu film is fabricated into a predetermined circuit. Thus, a second electrode 135 and a second wire 131 for the thin film capacitor 141 are formed. The first and second wires are connected by way of further wires to other planes.
Known multi-layer circuit packages involve the following drawbacks.
In a multi-layer circuit package in which a thin film capacitor is formed integrally, it is usually necessary to form a dielectric layer on a conductor. Generally, there is a problem that it is difficult for ceramics as the dielectric material to grow epitaxially on the conductor. This is because the lattice constant of a metal such as Cu, Ag or Al does not match the lattice constant of ceramics to be grown thereon. As a result, sputtered thin film of ceramics is not crystallized but tends to grow-in an amorphous state. The thin amorphous film of ceramics has lower dielectric constant compared with a thin epitaxial film grown in a crystalline state. Accordingly, the capacitance value of a capacitor manufactured by using the thin film is smaller than that manufactured by using a thin epitaxial film.
Further, in a case of using an easily oxidizable metal such as Cu or Al as the conductor, when oxide ceramics are sputtered thereon, the surface of a metal forming a first signal core is oxidized to form an oxide layer other than the thin ceramic film for instance. As a result, the thickness of the dielectric layer is increased to result in a problem of lowering the capacitance value.
Further, in the existent multi-layer circuit packages and the manufacturing methods thereof, a first signal core is formed as a circuit by patterning a conductor by means of photolithography and a thin film of dielectric material is formed on the first signal core. However, since it is difficult to completely remove a resist disposed for patterning without giving damage to the surface of the conductor, a residue is left. When a thin film of the dielectric material is formed on the surface of the conductor contaminated with organic residues such as a resist, this results in a problem of deteriorating the film quality which may cause lowering of the dielectric constant or generation of leak current.